Advanced lithographic techniques such as 193 nm immersion lithography have been developed to achieve high quality and smaller feature sizes in microlithography processes, for purposes of forming ever-smaller logic and memory transistors. It is important to achieve both smaller critical dimension (CD) in the imaged photoresist used in the microlithography process, and for the photoresists to provide both the lowest line edge roughness (LER) and line width roughness (LWR), while still retaining good process control tolerances such as high exposure latitude (EL) and a wide depth of focus (DOF).
To meet the challenges for resist materials raised by high resolution lithography, tailor-made photoacid generators (PAGs) with controlled acid diffusion and improved miscibility with polymers are very important. It has been found that the structure of the PAG anion plays a critical role in the overall performance of a photoresist by affecting the interaction of the photoacid generator with other photoresist components. These interactions, affect the diffusion characteristics of the photogenerated acid. PAG structure and size can therefore affect the homogenous distribution of the PAG in the photoresist film. Imaged photoresists can exhibit defects such as T-topping, foot formation and notching/undercut where the PAG is not uniformly distributed within the photoresist film.
While a variety of photoacid generators (PAGs) used for formulating photoresists are found in prior art, such as those disclosed in U.S. Pat. No. 7,304,175, a need remains for photoresist compositions including PAGs having greater diffusion control and attendant properties such as resist profile.